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CS 106A, Lecture 28 Final Exam Review 2

CS 106A, Lecture 28 Final Exam Review 2. Plan for today. Announcements HashMaps Classes Inheritance Interactors Closing Remarks. Plan for today. Announcements HashMaps Classes Inheritance Interactors Closing Remarks. Review: HashMaps.

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CS 106A, Lecture 28 Final Exam Review 2

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  1. CS 106A, Lecture 28Final Exam Review 2

  2. Plan for today • Announcements • HashMaps • Classes • Inheritance • Interactors • Closing Remarks

  3. Plan for today • Announcements • HashMaps • Classes • Inheritance • Interactors • Closing Remarks

  4. Review: HashMaps • A variable type that represents a collection of key-value pairs • You access values by key, and all keys are unique • Keys and values can be any type of object (use wrapper classes to store primitives) • Resizable – can add and remove pairs • Has a variety of methods you can use, including .containsKey, .put, .get, etc.

  5. HashMap Examples • Phone book: name -> phone number • Search engine: URL -> webpage • Dictionary: word -> definition • Bank: account # -> balance • Social Network: name -> profile • Counter: text -> # occurrences • And many more…

  6. Review: HashMap Operations • m.put(key, value); Adds a key/value pair to the map. m.put("Eric", "650-123-4567"); • Replaces any previous value for that key. • m.get(key) Returns the value paired with the given key. String phoneNum = m.get("Jenny"); // "867-5309" • Returns null if the key is not found. • m.remove(key);Removes thegiven key and its paired value. m.remove("Rishi"); • Has no effect if the key is not in the map. keyvalue "Jenny” → "867-5309" "Mehran" → "123-4567" "Marty" → "685-2181" "Chris” → "947-2176"

  7. Review: HashMap Operations • m.containsKey(key); Returns true if the key is in the map, false otherwise • m.size();Returns the number of key/value pairs in the map. • To iterate over a map: for (KeyType key : map.keySet()) { ValueType value = map.get(key); // Do something with key and/or value }

  8. What data structure should I use? • Use an array if… • Order matters for your information • You know how many elements you will store • You need the most efficiency • Use an ArrayListif… • Order matters for your information • You do not know how many elements you will store, or need to resize • You need to use ArrayList methods • Use a HashMap if… • Order doesn’t matter for your information • You need to store an association between two types of information • You do not know how many elements you will store, or need to resize • You need to use HashMap methods

  9. Practice: Anagrams • Write a program to find all anagrams of a word the user types. Type a word [Enter to quit]: scared Anagrams of scared: cadres cedars sacred scared • Assume you are given the following: • A dictionary.txt file containing words in the dictionary • A method private String sortLetters(String s) method that takes a string and returns the string with its characters alphabetically ordered. • How can a HashMap help us solve this problem?

  10. Key Idea: Anagrams • Every word has a sorted form where its letters are arranged into alphabetical order. "fare" "aefr" "fear" "aefr" "swell" "ellsw" "wells"  "ellsw" • Notice that anagrams have the same sorted form as each other.

  11. Anagrams Solution publicvoidrun() { HashMap<String, ArrayList<String>> anagrams = createAnagramsMap(); // prompt user for words and look up anagrams in map String word = readLine("Type a word [Enter to quit]: "); while(word.length() > 0) {     String sorted = sortLetters(word.toLowerCase()); if(anagrams.containsKey(sorted)) { println("Anagrams of " + word + ":"); println(anagrams.get(sorted));     } else{ println("No anagrams for " + word + ".");     }     word = readLine("Type a word [Enter to quit]: "); } }

  12. Anagrams Solution publicvoid run() { HashMap<String, ArrayList<String>> anagrams = createAnagramsMap(); // prompt user for words and look up anagrams in map String word = readLine("Type a word [Enter to quit]: "); while(word.length() > 0) {     String sorted = sortLetters(word.toLowerCase()); if (anagrams.containsKey(sorted)) { println("Anagrams of " + word + ":"); println(anagrams.get(sorted));     } else { println("No anagrams for " + word + ".");     }     word = readLine("Type a word [Enter to quit]: "); } }

  13. Anagrams Solution publicvoid run() { HashMap<String, ArrayList<String>> anagrams = createAnagramsMap(); // prompt user for words and look up anagrams in map String word = readLine("Type a word [Enter to quit]: "); while(word.length() > 0) {     String sorted = sortLetters(word.toLowerCase()); if (anagrams.containsKey(sorted)) { println("Anagrams of " + word + ":"); println(anagrams.get(sorted));     } else { println("No anagrams for " + word + ".");     } word = readLine("Type a word [Enter to quit]: "); } }

  14. Anagrams Solution publicvoid run() { HashMap<String, ArrayList<String>> anagrams = createAnagramsMap(); // prompt user for words and look up anagrams in map String word = readLine("Type a word [Enter to quit]: "); while(word.length() > 0) {     String sorted = sortLetters(word.toLowerCase()); if (anagrams.containsKey(sorted)) { println("Anagrams of " + word + ":"); println(anagrams.get(sorted));     } else { println("No anagrams for " + word + ".");     }     word = readLine("Type a word [Enter to quit]: "); } }

  15. Anagrams Solution publicvoid run() { HashMap<String, ArrayList<String>> anagrams = createAnagramsMap(); // prompt user for words and look up anagrams in map String word = readLine("Type a word [Enter to quit]: "); while(word.length() > 0) {     String sorted = sortLetters(word.toLowerCase()); if (anagrams.containsKey(sorted)) { println("Anagrams of " + word + ":"); println(anagrams.get(sorted));     } else { println("No anagrams for " + word + ".");     }     word = readLine("Type a word [Enter to quit]: "); } }

  16. Anagrams Solution publicvoidrun() { HashMap<String, ArrayList<String>> anagrams = createAnagramsMap(); // prompt user for words and look up anagrams in map String word = readLine("Type a word [Enter to quit]: "); while(word.length() > 0) {     String sorted = sortLetters(word.toLowerCase()); if(anagrams.containsKey(sorted)) { println("Anagrams of " + word + ":"); println(anagrams.get(sorted));     } else{ println("No anagrams for " + word + ".");     }     word = readLine("Type a word [Enter to quit]: "); } }

  17. Anagrams Solution, Part 2 // Returns a new map from a sorted word to all words created // from those letters - e.g. “acers” -> {“scare”, “cares”,...} privateHashMap<String, ArrayList<String>> createAnagramsMap() { HashMap<String, ArrayList<String>> anagrams = newHashMap<>(); try{ Scanner scanner = new Scanner(new File("res/dictionary.txt")); while(scanner.hasNext()) { String word = scanner.next(); String sorted = sortLetters(word); ...

  18. Anagrams Solution, Part 2 // Returns a new map from a sorted word to all words created // from those letters - e.g. “acers” -> {“scare”, “cares”,...} privateHashMap<String, ArrayList<String>> createAnagramsMap() { HashMap<String, ArrayList<String>> anagrams = newHashMap<>(); try { Scanner scanner = new Scanner(new File("res/dictionary.txt")); while (scanner.hasNext()) { String word = scanner.next(); String sorted = sortLetters(word); ...

  19. Anagrams Solution, Part 2 // Returns a new map from a sorted word to all words created // from those letters - e.g. “acers” -> {“scare”, “cares”,...} privateHashMap<String, ArrayList<String>> createAnagramsMap() { HashMap<String, ArrayList<String>> anagrams = newHashMap<>(); try { Scanner scanner = new Scanner(new File("res/dictionary.txt")); while (scanner.hasNext()) { String word = scanner.next(); String sorted = sortLetters(word); ...

  20. Anagrams Solution, Part 2 // Returns a new map from a sorted word to all words created // from those letters - e.g. “acers” -> {“scare”, “cares”,...} privateHashMap<String, ArrayList<String>> createAnagramsMap() { HashMap<String, ArrayList<String>> anagrams = newHashMap<>(); try { Scanner scanner = new Scanner(new File("res/dictionary.txt")); while (scanner.hasNext()) { String word = scanner.next(); String sorted = sortLetters(word); ...

  21. Anagrams Solution, Part 2 // Returns a new map from a sorted word to all words created // from those letters - e.g. “acers” -> {“scare”, “cares”,...} privateHashMap<String, ArrayList<String>> createAnagramsMap() { HashMap<String, ArrayList<String>> anagrams = newHashMap<>(); try{ Scanner scanner = new Scanner(new File("res/dictionary.txt")); while(scanner.hasNext()) { String word = scanner.next(); String sorted = sortLetters(word); ...

  22. Anagrams Solution, Part 2 ArrayList<String> words; if (anagrams.containsKey(sorted)) { words = anagrams.get(sorted); } else { words = newArrayList<>(); } words.add(word); anagrams.put(sorted, words); } scanner.close(); } catch(IOException ex) { println("Error reading file."); } return anagrams; }

  23. Anagrams Solution, Part 2 ArrayList<String> words; if (anagrams.containsKey(sorted)) { words = anagrams.get(sorted); } else { words = newArrayList<>(); } words.add(word); anagrams.put(sorted, words); } scanner.close(); } catch (IOException ex) { println("Error reading file."); } return anagrams; }

  24. Anagrams Solution, Part 2 ArrayList<String> words; if (anagrams.containsKey(sorted)) { words = anagrams.get(sorted); } else { words = newArrayList<>(); } words.add(word); anagrams.put(sorted, words); } scanner.close(); } catch (IOException ex) { println("Error reading file."); } return anagrams; }

  25. Anagrams Solution, Part 2 ArrayList<String> words; if (anagrams.containsKey(sorted)) { words = anagrams.get(sorted); } else { words = newArrayList<>(); } words.add(word); anagrams.put(sorted, words); } scanner.close(); } catch (IOException ex) { println("Error reading file."); } return anagrams; }

  26. Anagrams Solution, Part 2 ArrayList<String> words; if (anagrams.containsKey(sorted)) { words = anagrams.get(sorted); } else { words = newArrayList<>(); } words.add(word); anagrams.put(sorted, words); } scanner.close(); } catch(IOException ex) { println("Error reading file."); } return anagrams; }

  27. Plan for today • Announcements • HashMaps • Classes • Inheritance • Interactors • Closing Remarks

  28. What Is A Class? A class defines a new variable type.

  29. Classes Are Like Blueprints iPod (variable) #1 state: song = "1,000,000 Miles" volume = 17 battery life = 2.5 hrs behavior: power on/off change station/song change volume choose random song iPod (variable) #2 state: song = "Letting You" volume = 9 battery life = 3.41 hrs behavior: power on/off change station/song change volume choose random song iPod (variable) #3 state: song = "Discipline" volume = 24 battery life = 1.8 hrs behavior: power on/off change station/song change volume choose random song iPod blueprint (class) state:current song volume battery life behavior:power on/off change station/song change volume choose random song constructs

  30. Creating A New Class • What information is inside this new variable type? These are its instance variables. • What can this new variable type do? These are its public methods. • How do you create a variable of this type? This is the constructor.

  31. Defining Methods In Classes ba1 Methods defined in classes can be called on an instance of that class. When one of these methods executes, it can reference that object’s copy of instance variables. ba1.deposit(0.20); ba2.deposit(1000.00); This means calling one of these methods on different objects has different effects. name = "Marty" balance = 1.45 deposit(amount) { balance += amount; } ba2 name = "Mehran" balance = 901000.00 deposit(amount) { balance += amount; }

  32. Constructors BankAccount ba1 = newBankAccount(); BankAccount ba2 = newBankAccount(“Nick”, 50); The constructor is executed when a new object is created.

  33. Example: BankAccount publicclassBankAccount { // Step 1: the data inside a BankAccount private String name; privatedouble balance; // Step 2: the things a BankAccount can do (omitted) // Step 3: how to create a BankAccount publicBankAccount(String accountName, doublestartBalance) { name = accountName; balance = startBalance; } publicBankAccount(String accountName) { name = accountName; balance = 0; } }

  34. Using Constructors ba1 BankAccount ba1 = new BankAccount("Marty", 1.25); BankAccount ba2 = new BankAccount("Mehran", 900000.00); • When you call a constructor (with new): • Java creates a new object of that class. • The constructor runs, on that new object. • The newly created object is returned to your program. name = "Marty" balance = 1.25 BankAccount(nm, bal) { name = nm; balance = bal; } ba2 name = "Mehran" balance = 900000.00 BankAccount(nm, bal) { name = nm; balance = bal; }

  35. Practice: Airplane! Let’s write a class called Airplane that implements functionality for boarding/unboarding passengers from a plane. Airplane plane = new Airplane(100); while (!plane.isFull()) { String passengerName = readLine("Name: "); booleanpriority = readBoolean("Priority? "); plane.boardPassenger(passengerName, priority); } // fly... while (!plane.isEmpty()) { String passengerName = plane.unboardPassenger(); println("Unboarded " + passengerName); }

  36. Practice: Airplane! Let’s write a class called Airplane that implements functionality for boarding/unboarding passengers from a plane. It should implement the following methods: // Constructor should take 1 parameter (plane capacity) /** Boards 1 passenger, at front or back **/ publicvoidboardPassenger(String name, booleanpriority); publicbooleanisFull(); publicbooleanisEmpty(); /** Unboards and returns next passenger **/ publicStringunboardPassenger();

  37. Creating A New Class • What information is inside this new variable type? These are its instance variables. • What can this new variable type do? These are its public methods. • How do you create a variable of this type? This is the constructor.

  38. Practice: Airplane! public class Airplane { private ArrayList<String> passengers; private intcapacity; ...

  39. Creating A New Class • What information is inside this new variable type? These are its instance variables. • What can this new variable type do? These are its public methods. • How do you create a variable of this type? This is the constructor.

  40. boardPassenger ... public void boardPassenger(String name, booleanpriority) { if (!isFull()) { if (priority) {passengers.add(0, name); } else { passengers.add(name); } } } ...

  41. isFull ... public booleanisFull() { return capacity == passengers.size(); } ...

  42. isEmpty ... public booleanisEmpty() { return passengers.isEmpty(); } ...

  43. unboardPassenger ... public String unboardPassenger() { if (!isEmpty()) { returnpassengers.remove(0); } return null; } ...

  44. Creating A New Class • What information is inside this new variable type? These are its instance variables. • What can this new variable type do? These are its public methods. • How do you create a variable of this type? This is the constructor.

  45. Practice: Airplane! // Private instance variables private ArrayList<String> passengers; private intcapacity; public Airplane(intnumSeats) { capacity = numSeats; passengers = newArrayList<>(); } ...

  46. Plan for today • Announcements • HashMaps • Classes • Inheritance • Interactors • Closing Remarks

  47. Review: Inheritance Inheritance lets us relate our variable types to one another.

  48. Inheritance Variable types can seem to “inherit” from each other. We don’t want to have to duplicate code for each one! Employee Programmer Karel Programmer

  49. Using Inheritance public class Nameextends Superclass{ • Example: public class Programmer extends Employee { ... } • By extending Employee, this tells Java that Programmer can do everything an Employee can do, plus more. • Programmer automatically inherits all of the code from Employee! • The superclass is Employee, the subclass is Programmer.

  50. Example: Programmer publicclass Programmer extends Employee { privateinttimeCoding; ... publicvoid code() {timeCoding += 10; } } ... Programmer rishi = new Programmer(“Rishi”); rishi.code(); // from Programmer rishi.promote(); // from Employee!

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